Bring a large pot of salted water to a boil. Add the rigatoni and cook until al dente, about 11 minutes. Drain and set aside.

While the pasta cooks, heat the olive oil in a large skillet over medium-high heat. Add the Italian sausage, breaking it into small pieces with a spoon. Cook until browned and cooked through, about 6 to 8 minutes.

Add the chopped onion to the skillet and sauté until softened, about 4 minutes. Stir in the minced garlic and cook for another 30 seconds until fragrant.

Pour in the crushed tomatoes and chicken broth. Stir in the oregano, basil, red pepper flakes if using, salt, and pepper. Bring the sauce to a simmer, reduce heat to medium-low, and let it cook for 10 minutes to develop flavor.

Add the cooked rigatoni to the sauce and toss gently to coat evenly. Stir in the grated Parmesan cheese until melted and combined.

Remove from heat and let the pasta rest for a couple of minutes to thicken the sauce slightly.

Serve hot, garnished with fresh basil leaves and extra Parmesan cheese if desired.